How to create a variable name from the value of a string in Ruby on Rails?

Question

I want to create an instance variable in a controller to be used in the view:

foo = "bar"
instance_variable_set("#{foo}", "cornholio")

In the view, use @bar so that:

@bar => "cornholio"

This generates an error: 'bar' is not allowed as an instance variable name

Working in Rails 3.1

score 39 · Accepted Answer · edited May 23 '17 at 12:16

39

This instance_variable_set("#{foo}", "cornholio") needs to read instance_variable_set("@#{foo}", "cornholio")

Based on this post. Just tried it in my irb for Ruby 1.93; the post is from 2009.

edited May 23 '17 at 12:16

Community

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answered Mar 08 '12 at 02:29

ScottJShea

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seems like a really common mistake that could be auto-corrected by prepending a `@` if it didn't exist. – Vlad the Impala Mar 09 '13 at 02:16

score 7 · Answer 2 · answered Mar 08 '12 at 09:58

7

In Ruby, instance variable names always have to start with an @ sigil.

answered Mar 08 '12 at 09:58

Jörg W Mittag

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+1 for terminology! Interestingly, http://en.wikipedia.org/wiki/Sigil_%28magic%29 came before http://en.wikipedia.org/wiki/Sigil_%28computer_programming%29 when Googling. – Andrew Grimm Mar 08 '12 at 22:48
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And that's exactly the reason why one could have thought that a method like instance_variable_set takes care of adding the "@"... – Rip-Off Jan 28 '14 at 15:24

score 0 · Answer 3 · answered May 21 '20 at 23:47

I was looking for the answer for the same question but with an other thought. Because other people might ending up here looking for my answer here my question and solution:

I want to cal t(key, interpolation_var: value) in a method. where interpolation _var: is different per translation. solution(I have removed all non important information so only the solution to the problem is available. that's why the method looks unusefull :) ):

def some_function(key, interpolation_var, value)
  t(key, :#{interpolation_var} => value)
end

How to create a variable name from the value of a string in Ruby on Rails?

3 Answers3